This invention relates to methods and apparatus for running, operating, and retrieving devices used in drilling and completing wells at an underwater location. More particularly, the invention relates to hydraulically actuated tools for running, operating, and retrieving various subsea well completion equipment such as packoffs, bowl protectors, casing heads, and casing hangers, and to methods for actuating these tools. United States patents on these subjects can be found in class 166 of the United States Patent Classification System.
Prior to the present invention, in the process of drilling and completing subsea oil and gas wells it has been conventional practice to employ external hydraulic lines or the inner bore of the drill pipe string to conduct hydraulic control fluid from the drilling vessel or platform to the subsea wellhead for actuating various well tools at that remote location. Although external hydraulic lines are generally successful these lines are cumbersome, they are easily damaged, their cost is significant, and their use usually requires a separate source of power and controls therefor. Using the bore of the drill string also is not considered desirable, especially because of the time involved in installing the kelly assembly. Furthermore, when the drill string is employed for this purpose it must be plugged at the bottom, and this prevents the hydraulic fluid from draining as the string is broken apat during retrieval from the well, with the result that the hydraulic fluid spills onto the work area. Although retrievable plugs can be used in the drill string, such use requires an extra, and of course costly, trip into and out of the well to retrieve the plug.